U.S. patent application number 11/991107 was filed with the patent office on 2009-11-12 for semiconductor nanoparticle and method of producing the same.
This patent application is currently assigned to NATIONAL UNIVERSITY CORPORATION NAGOYA UNIVERSITY. Invention is credited to Tomohiro Adachi, Akihiko Kudo, Susumu Kuwabata, Bunsho Ohtani, Miwa Sakuraoka, Tamaki Shibayama, Tsukasa Torimoto.
Application Number | 20090278094 11/991107 |
Document ID | / |
Family ID | 37808831 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090278094 |
Kind Code |
A1 |
Torimoto; Tsukasa ; et
al. |
November 12, 2009 |
Semiconductor nanoparticle and method of producing the same
Abstract
The present invention provides semiconductor nanoparticles which
emit light at room temperature and include a sulfide or oxide
containing zinc, a Group 11 element in the periodic table, and a
Group 13 element in the periodic table as a main component or a
sulfide or oxide containing a Group 11 element in the periodic
table and a Group 13 element in the periodic table as a main
component. For example, the semiconductor nanoparticles are
represented by Zn.sub.(1-2x)In.sub.xAg.sub.xS
(O<x.ltoreq.0.5).
Inventors: |
Torimoto; Tsukasa;
(Nagoya-shi, JP) ; Kuwabata; Susumu; (Ibaraki-shi,
JP) ; Ohtani; Bunsho; (Hokkaido, JP) ;
Shibayama; Tamaki; (Hokkaido, JP) ; Kudo;
Akihiko; (Kawasaki-shi, JP) ; Sakuraoka; Miwa;
(Sapporo-shi, JP) ; Adachi; Tomohiro;
(Tsushima-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NATIONAL UNIVERSITY CORPORATION
NAGOYA UNIVERSITY
NAGOYA-SHI
JP
OSAKA UNIVERSITY
SUITA-SHI
JP
NATIONAL UNIVERSITY CORPORATION HOKKAIDO UNIVERSITY
SAPPORO-SHI
JP
TOKYO UNIVERSITY OF SCIENCE EDUCATIONAL FOUNDATION
ADMINISTRATIVE ORGANIZATION
TOKYO
JP
|
Family ID: |
37808831 |
Appl. No.: |
11/991107 |
Filed: |
August 30, 2006 |
PCT Filed: |
August 30, 2006 |
PCT NO: |
PCT/JP2006/317072 |
371 Date: |
April 18, 2008 |
Current U.S.
Class: |
252/501.1 ;
977/813 |
Current CPC
Class: |
B82Y 30/00 20130101;
C09K 11/623 20130101; B82Y 20/00 20130101 |
Class at
Publication: |
252/501.1 ;
977/813 |
International
Class: |
H01B 1/02 20060101
H01B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2005 |
JP |
2005-255656 |
Claims
1. A semiconductor nanoparticle which emits light at room
temperature, comprising a sulfide or oxide containing zinc, a Group
11 element in the periodic table, and a Group 13 element in the
periodic table as a main component or a sulfide or oxide containing
a Group 11 element in the periodic table and a Group 13 element in
the periodic table as a main component.
2. A semiconductor nanoparticle which emits light at room
temperature, comprising a sulfide or oxide containing zinc, a Group
11 element in the periodic table, and a Group 13 element in the
periodic table as a main component or a sulfide or oxide containing
a Group 11 element in the periodic table and a Group 13 element in
the periodic table as a main component, the surface of the
nanoparticle being modified with a lipid-soluble compound.
3. A semiconductor nanoparticle which emits light at room
temperature and is produced by mixing a zinc salt, a salt of a
Group 11 element in the periodic table, a salt of a Group 13
element in the periodic table, and a ligand containing sulfur or
oxygen as a coordinating element or mixing a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element to form a complex, heating the complex to form
a heat-treated product, and heating the heat-treated product
together with a lipid-soluble compound.
4. A semiconductor nanoparticle which emits light at room
temperature and is produced by mixing a zinc salt, a salt of a
Group 11 element in the periodic table, a salt of a Group 13
element in the periodic table, and a ligand containing sulfur or
oxygen as a coordinating element or mixing a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element to form a complex, and heating the complex
together with a lipid-soluble compound.
5. The semiconductor nanoparticle according to claim 3, wherein the
zinc salt, the salt of the Group 11 element in the periodic table,
the salt of the Group 13 element in the periodic table, and the
ligand containing sulfur or oxygen as a coordinating element are
mixed so that the ratio between the numbers of atoms of zinc, the
Group 11 element in the periodic table, and the Group 13 element in
the periodic table is (1-2x):x:x (wherein 0<x<0.5) or the
salt of the Group 11 element in the periodic table, the salt of the
Group 13 element in the periodic table, and the ligand containing
sulfur or oxygen as a coordinating element are mixed so that the
ratio between the numbers of atoms of the Group 11 element in the
periodic table and the Group 13 element in the periodic table is
1:1.
6. The semiconductor nanoparticle according to claim 5, wherein the
property of the luminescent color after excitation with exciting
light varies according to the x value.
7. The semiconductor nanoparticle according to claim 2, wherein the
lipid-soluble compound is a nitrogen-containing compound having a
hydrocarbon group having 4 to 20 carbon atoms.
8. The semiconductor nanoparticle according to claim 1, wherein the
Group 11 element in the periodic table is Ag or Cu.
9. The semiconductor nanoparticle according to claim 1, wherein the
Group 13 element in the periodic table is Ga or In.
10. A method of producing a semiconductor nanoparticle which emits
light at room temperature, comprising mixing a zinc salt, a salt of
a Group 11 element in the periodic table, a salt of a Group 13
element in the periodic table, and a ligand containing sulfur or
oxygen as a coordinating element or mixing a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element to form a complex, heating the complex to form
a heat-treated product, and heating the heat-treated product
together with a lipid-soluble compound.
11. A method of producing a semiconductor nanoparticle which emits
light at room temperature, comprising mixing a zinc salt, a salt of
a Group 11 element in the periodic table, a salt of a Group 13
element in the periodic table, and a ligand containing sulfur or
oxygen as a coordinating element or mixing a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element to form a complex, and heating the complex
together with a lipid-soluble compound.
12. The method according to claim 10, wherein the zinc salt, the
salt of the Group 11 element in the periodic table, the salt of the
Group 13 element in the periodic table, and the ligand containing
sulfur or oxygen as a coordinating element are mixed so that the
ratio between the numbers of atoms of zinc, the Group 11 element in
the periodic table, and the Group 13 element in the periodic table
is (1-2x):x:x (wherein 0<x<0.5) or the salt of the Group 11
element in the periodic table, the salt of the Group 13 element in
the periodic table, and the ligand containing sulfur or oxygen as a
coordinating element are mixed so that the ratio between the
numbers of atoms of the Group 11 element in the periodic table and
the Group 13 element in the periodic table is 1:1.
Description
TECHNICAL FIELD
[0001] The present invention relates to semiconductor nanoparticles
and a method of producing the same, and specifically to
semiconductor nanoparticles which emit light at room temperature
and a method of producing the same.
BACKGROUND ART
[0002] There have been known semiconductor nanoparticles of CdS,
CdSe, CdTe, PbS, PbSe, and the like (refer to, for example, Patent
Documents 1 and 2). As the diameter of such semiconductor
nanoparticles decreases to about 10 nm or less, the semiconductor
nanoparticles exhibit physiochemical properties completely
different from those of large bulk semiconductor particles due to a
quantum size effect. In the semiconductor nanoparticles of such a
size, the degeneracy of the energy bands that is observed in bulk
semiconductor particles is removed to discretize the energy bands,
and the band gap energy increases as the particle size decreases.
Further, an emission spectrum of the semiconductor nanoparticles is
greatly changed in such a manner that the emission peak position of
the band gap shifts to the short-wavelength side as the particle
size decreases. In addition, the emission wavelength can be freely
controlled by controlling the size of the semiconductor
nanoparticles, and the semiconductor nanoparticles are several
orders more stable than an organic dye under irradiation with
exciting light. The emission peak width of the semiconductor
nanoparticles is sufficiently narrower than that of an organic dye.
Therefore, at present, luminescent materials have been actively
developed using semiconductor nanoparticles. In particular, the use
as a marker for identifying specified molecules such as biological
molecules reaches the stage of practical application.
[0003] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2004-243507
[0004] Patent Document 2: Japanese Unexamined Patent Application
Publication No. 2004-352594
DISCLOSURE OF INVENTION
[0005] In previous researches, nanoparticles having an intended
emission peak wavelength have been formed by precisely controlling
the diameter of the semiconductor nanoparticles. However, intended
semiconductor particles are particles of CdS, CdSe, CdTe, PbS, and
PbSe and contain an element having high toxicity, and a synthesis
precursor thereof also has high toxicity. Although semiconductor
nanoparticles of InP or the like, which has relatively low
toxicity, have been synthesized, the precursor used is a phosphorus
compound having very high toxicity. Among these nanoparticles,
semiconductor nanoparticles having low toxicity and produced using
a precursor having low toxicity in the production process are
demanded.
[0006] The present invention has been achieved for complying with
the demand, and an object of the present invention is to provide
semiconductor nanoparticles which sufficiently emit light without
using a compound with high toxicity in a production process.
Another object is to provide a method of relatively easily
producing the semiconductor nanoparticles.
[0007] As a result of intensive research for achieving the objects,
the inventors have found that semiconductor nanoparticles composed
of a sulfide or oxide as a main component emit light at room
temperature, leading to the completion of the present
invention.
[0008] In a first aspect of the present invention, semiconductor
nanoparticles which emit light at room temperature include a
sulfide or oxide containing zinc and a Group 11 element and a Group
13 element in the periodic table as a main component or a sulfide
or oxide containing a Group 11 element and a Group 13 element in
the periodic table as a main component. The semiconductor
nanoparticles of the present invention may emit light at a
temperature other than room temperature as long as they emit light
at room temperature. In the specification, "room temperature"
represents 15.degree. C. to 25.degree. C. The term "light emission"
represents that electrons absorb energy (e.g., light energy,
electric energy, chemical energy, thermal energy, or the like) to
be excited, and then the excited electrons emit light energy when
being inactivated regardless of whether fluorescence or
phosphorescence. The energy absorbed is preferably light energy or
electric energy.
[0009] Examples of the Group 11 element in the periodic table
include, but are not limited thereto, Cu. Ag, and Au. Among these
elements, Cu and Ag are preferred, and Ag is particularly
preferred. Examples of the Group 13 element in the periodic table
include, but are not limited thereto, Ga, In, and Tl. Among these
elements, Ga and In are preferred, and In is particularly
preferred.
[0010] In a second aspect of the present invention, semiconductor
nanoparticles which emit light at room temperature include a
sulfide or oxide containing zinc and a Group 11 element and a Group
13 element in the periodic table as a main component or a sulfide
or oxide containing a Group 11 element and a Group 13 element in
the periodic table as a main component, the surfaces of the
particles being modified with a lipid-soluble compound.
[0011] Since the Group 11 and 13 elements are the same as in the
first aspect of the present invention, description thereof is
omitted. The lipid-soluble compound may be any compound as long as
it can be bonded to the surfaces of the particles composed of the
sulfide or oxide as a main component. Examples of the bond type
include, but are not limited thereto, chemical bonds such as a
covalent bond, an ionic bond, a coordination bond, a hydrogen bond,
and a Van der Waals bond. Typical examples of the lipid-soluble
compound include nitrogen-containing compounds each containing a
hydrocarbon group having 4 to 20 carbon atoms, sulfur-containing
compounds each containing a hydrocarbon group having 4 to 20 carbon
atoms, and oxygen-containing compounds each containing a
hydrocarbon group having 4 to 20 carbon atoms. Examples of the
hydrocarbon group having 4 to 20 carbon atoms include saturated
aliphatic hydrocarbon groups; such as a n-butyl group, an isobutyl
group, a n-pentyl group, a n-hexyl group, an octyl group, a decyl
group, a dodecyl group, a hexadecyl group, and an octadecyl group;
unsaturated aliphatic hydrocarbon groups, such as an oleyl group;
alicyclic hydrocarbon groups, such as a cyclopentyl group and a
cyclohexyl group; and aromatic hydrocarbon groups, such as a phenyl
group, a benzyl group, a naphthyl group, and a naphthylmethyl
group. Among these groups, the saturated aliphatic hydrocarbon
groups and the unsaturated aliphatic hydrocarbon groups are
preferred. Examples of the nitrogen-containing compounds include
amines and amides, examples of the sulfur-containing compounds
include thiols, and examples of the oxygen-containing compounds
include fatty acids. Among these lipid-soluble compounds, the
nitrogen-containing compounds each having a hydrocarbon group
having 4 to 20 carbon atoms are preferred. Preferred examples of
such compounds include alkylamines such as n-butylamine,
isobutylamine, n-pentylamine, n-hexylamine, octylamine, decylamine,
dodecylamine, hexadecylamine, and octadecylamine; and alkenylamines
such as oleylamine.
[0012] In a third aspect of the present invention, semiconductor
nanoparticles which emit light at room temperature are produced by
mixing a zinc salt, a salt of a Group 11 element in the periodic
table, a salt of a Group 13 element in the periodic table, and a
ligand containing sulfur or oxygen as a coordinating element or
mixing a salt of a Group 11 element in the periodic table, a salt
of a Group 13 element in the periodic table, and a ligand
containing sulfur or oxygen as a coordinating element to form a
complex, heating the complex to form a heat-treated product, and
heating the heat-treated product together with a lipid-soluble
compound.
[0013] Since the Group 11 and 13 elements are the same as in the
first aspect of the present invention, and the lipid-soluble
compound is the same as in the second aspect of the present
invention, description thereof is omitted. Examples of the ligand
containing sulfur as a coordinating element include, but are not
limited thereto, .beta.-dithiones such as 2,4-pentanedithione;
dithiols such as 1,2-bis(trifluoromethyl)ethylene-1,2-dithiol; and
diethyldithiocarbamates. Examples of the ligand containing oxygen
as a coordinating element include, but are not limited thereto,
.beta.-diketones such as acetylacetone and hexafluoroacetylacetone;
and tropolone.
[0014] The conditions for heat treatment of the complex vary
according to the raw materials used and thus cannot be determined
absolutely. However, in general, the reaction temperature is
preferably set in the range of 100.degree. C. to 300.degree. C. and
more preferably in the range of 150.degree. C. to 200.degree. C.
The temperature represents the temperature of a heating device for
heating a reaction vessel. The preferred reaction time range also
varies according to the reaction temperature, but in general, the
reaction time is preferably set in the range of several seconds to
several hours and more preferably in the range of 1 to 60
minutes.
[0015] The conditions for heating the heat-treated product together
with the lipid-soluble compound vary according to the raw materials
used and thus cannot be determined absolutely. However, in general,
the reaction temperature is preferably set in the range of
100.degree. C. to 300.degree. C. and more preferably in the range
of 150.degree. C. to 200.degree. C. As the reaction temperature
decreases, the emission peak wavelength tends to shift to the
short-wavelength side. Although the cause for this is not known, a
conceivable cause is that at a lower temperature, the growth of
particles is suppressed, and thus smaller nanoparticles are
produced, thereby increasing the degree of the quantum size effect.
The temperature represents the temperature of a heating device for
heating a reaction vessel. The preferred reaction time range also
varies according to the reaction temperature, but in general, the
reaction time is preferably set in the range of several seconds to
several hours and more preferably set in the range of 1 to 60
minutes. As the reaction time increases, the emission peak
wavelength tends to shift to the long-wavelength side. Although the
cause for this is not known, a conceivable cause is that the growth
of particles is accelerated by increasing the reaction time, and
thus larger nanoparticles are produced, thereby decreasing the
degree of the quantum size effect.
[0016] In a fourth aspect of the present invention, semiconductor
nanoparticles which emit light at room temperature are produced by
mixing a zinc salt, a salt of a Group 11 element in the periodic
table, a salt of a Group 13 element in the periodic table, and a
ligand containing sulfur or oxygen as a coordinating element or
mixing a salt of a Group 11 element in the periodic table, a salt
of a Group 13 element in the periodic table, and a ligand
containing sulfur or oxygen as a coordinating element to form a
complex, and heating the complex together with a lipid-soluble
compound. In the third aspect of the present invention, the step of
heat-treating the complex and the step of heating the heat-treated
product together with the lipid-soluble compound are sequentially
performed (sequential method). However, in the fourth aspect of the
present invention, the step of heat-treating the complex is
omitted, and both the complex and the lipid-soluble compound are
heated to heat-treat the complex and react the heat-treated product
with the lipid-soluble compound at the same time (simultaneous
method).
[0017] Since the Group 11 and 13 elements are the same as in the
first aspect of the present invention, the lipid-soluble compound
is the same as in the second aspect of the present invention, and
the ligand containing sulfur or oxygen as a coordinating element is
the same as in the third aspect of the present invention,
description thereof is omitted. The conditions for heating the
complex together with the lipid-soluble compound vary according to
the raw materials used and thus cannot determined absolutely.
However, in general, the reaction temperature is preferably set in
the range of 100.degree. C. to 300.degree. C. and more preferably
set in the range of 150.degree. C. to 200.degree. C. As the
reaction temperature decreases, the emission peak wavelength tends
to shift to the short-wavelength side. Although the cause for this
is not known, a conceivable cause is that at a lower temperature,
the growth of particles is suppressed, and thus smaller
nanoparticles are produced, thereby increasing the degree of the
quantum size effect. The temperature represents the temperature of
a heating device for heating a reaction vessel. The preferred
reaction time range also varies according to the reaction
temperature, but in general, the reaction time is preferably set in
the range of several seconds to several hours and more preferably
in the range of 1 to 60 minutes. As the reaction time increases,
the emission peak wavelength tends to shift to the long-wavelength
side. Although the cause for this is not known, a conceivable cause
is that the growth of particles is accelerated by increasing the
reaction time, and thus larger nanoparticles are produced, thereby
decreasing the degree of the quantum size effect.
[0018] Since the third and fourth aspects of the present invention
correspond to a so-called product-by-process claim, it is
understood that the technical scope of the present invention
includes not only semiconductor nanoparticles produced through the
process described in the claims but also semiconductor
nanoparticles produced through a process other than the process
described in the claims as long as they are substantially the same
as the semiconductor nanoparticles produced through the process
described in the claims. In the first to fourth aspects of the
present invention, the particle size of the semiconductor
nanoparticles with which the quantum size effect appears depends on
the composition, but the particle size is preferably 100 nm or
less, more preferably 50 nm or less, and most preferably 20 nm or
less.
[0019] In a fifth aspect of the present invention, a method of
producing semiconductor nanoparticles which emit light at room
temperature includes mixing a zinc salt, a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element or mixing a salt of a Group 11 element in the
periodic table, a salt of a Group 13 element in the periodic table,
and a ligand containing sulfur or oxygen as a coordinating element
to form a complex, heating the complex to form a heat-treated
product, and heating the heat-treated product together with a
lipid-soluble compound.
[0020] Since the Group 11 and 13 elements are the same as in the
first aspect of the present invention, the lipid-soluble compound
is the same as in the second aspect of the present invention, and
the ligand containing sulfur or oxygen as a coordinating element is
the same as in the third aspect of the present invention,
description thereof is omitted. Also, the conditions for heat
treatment of the complex and the conditions for heating the
heat-treated product together with the lipid-soluble compound are
the same as in the third aspect of the present invention,
description thereof is omitted.
[0021] In a sixth aspect of the present invention, a method of
producing semiconductor nanoparticles which emit light at room
temperature includes mixing a zinc salt, a salt of a Group 11
element in the periodic table, a salt of a Group 13 element in the
periodic table, and a ligand containing sulfur or oxygen as a
coordinating element or mixing a salt of a Group 11 element in the
periodic table, a salt of a Group 13 element in the periodic table,
and a ligand containing sulfur or oxygen as a coordinating element
to form a complex, and heating the complex together with a
lipid-soluble compound.
[0022] Since the Group 11 and 13 elements are the same as in the
first aspect of the present invention, the lipid-soluble compound
is the same as in the second aspect of the present invention, and
the ligand containing sulfur or oxygen as a coordinating element is
the same as in the third aspect of the present invention. Also, the
conditions for heating the complex together with the lipid-soluble
compound are the same as in the fourth aspect of the present
invention.
[0023] In the first to sixth aspects of the present invention, the
zinc salt, the salt of the Group 11 element in the periodic table,
the salt of the Group 13 element in the periodic table, and the
ligand containing sulfur or oxygen as a coordinating element are
preferably mixed so that the atomic number ratio (=molar ratio)
between zinc, the Group 11 element in the periodic table, and the
Group 13 element in the periodic table is (1-2x):x:x (wherein
0<x.ltoreq.0.5). The semiconductor nanoparticles of the present
invention have the property that the luminescent color after
excitation with exciting light varies according to the x value.
Therefore, the semiconductor nanoparticles which emit light of a
desired color can be produced by appropriately setting the x value.
When the x value is 0.5, the ratio of the number of zinc atoms is
zero. This means that the Group 11 element and the Group 13 element
in the periodic table are mixed at a ratio between the numbers of
atoms of 1:1.
[0024] In the first to fourth aspects of the present invention,
zinc and the Group 11 element and the Group 13 element in the
periodic table are used in the process for producing the
semiconductor nanoparticles, and thus an element with high
toxicity, such Cd or the like, is not used unlike in a conventional
process. Therefore, the semiconductor nanoparticles can be produced
in a safe environment. Since the semiconductor nanoparticles
satisfactorily emit light at room temperature, they are promising
as a material for vital staining dyes and optical devices. In
particular, the color of emitted light can be controlled to be any
one of various colors only by changing the ratio between the
numbers of atoms of zinc, the Group 11 element in the periodic
table, and the Group 13 element in the periodic table, and the
nanoparticles can be expected to be used in various technical
fields.
[0025] In each of the methods of producing semiconductor
nanoparticles in the fifth and sixth aspects of the present
invention, zinc and the Group 11 element and the Group 13 element
in the periodic table are used in the process for producing the
semiconductor nanoparticles, and thus an element with high
toxicity, such Cd or the like, is not used unlike in a conventional
process. Therefore, the semiconductor nanoparticles can be produced
in a safe environment. Since the semiconductor nanoparticles
produced in the production method satisfactorily emit light at room
temperature, they are promising as a material for vital staining
dyes and optical devices. In particular, the color of emitted light
can be controlled to be any one of various colors only by changing
the ratio between the numbers of atoms of zinc, the Group 11
element in the periodic table, and the Group 13 element in the
periodic table, and the nanoparticles can be expected to be used in
various technical fields.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a graph showing emission spectra of
hexadecylamine-modified nanoparticles in 1-butanol.
[0027] FIG. 2 is a photograph showing TEM images of
hexadecylamine-modified nanoparticles.
[0028] FIG. 3 is a graph showing a particle size distribution of
hexadecylamine-modified nanoparticles.
[0029] FIGS. 4(a) and 4(b) are graphs showing excitation spectra
and emission spectra, respectively, of oleylamine-modified
nanoparticles dissolved in oleylamine.
[0030] FIG. 5 is a graph showing emission spectra of
oleylamine-modified nanoparticles precipitated in oleylamine.
[0031] FIGS. 6(a) and 6(b) are graphs showing absorption spectra
and emission spectra, respectively, of oleylamine-modified
nanoparticles dissolved in chloroform and oleylamine.
[0032] FIG. 7 is a graph showing emission spectra of
oleylamine-modified nanoparticles produced with different chemical
modification times.
[0033] FIG. 8 is a graph showing emission spectra (solvent:
chloroform) of amine-modified nanoparticles produced at different
chemical modification temperatures.
[0034] FIG. 9 is a graph showing emission spectra (solvent:
chloroform) of amine-modified nanoparticles produced by different
heat treatment methods, in which a solid line shows a simultaneous
method and a dotted line shows a sequential method.
[0035] FIG. 10 is a graph illustrating XRD patterns of
Zn.sub.1-2xIn.sub.xAg.sub.xS.sub.2 nanoparticles.
[0036] FIG. 11 is a graph illustrating XRD patterns of ZnS in
different crystal systems.
[0037] FIG. 12 is a graph illustrating XRD patterns of AgInS.sub.2
in different crystal systems.
[0038] FIG. 13 is a graph showing a relation between the x value
and emission peak position of Zn.sub.1-2xIn.sub.xAg.sub.xS
nanoparticles.
[0039] FIGS. 14(a) and 14(b) are graphs showing an absorption
spectrum and an emission spectrum, respectively, of
oleylamine-modified nanoparticles dissolved in chloroform.
BEST MODE FOR CARRYING OUT THE INVENTION
[0040] Best modes for carrying out the invention will be described
in detail with reference to examples.
EXAMPLE 1
[0041] A 0.1 moldm.sup.-3 aqueous solution of sodium
diethyldithiocarbamate was added to an aqueous solution (metal ion
concentration 0.1 moldm.sup.-3) containing Zn(NO.sub.3).sub.2,
In(NO.sub.3).sub.3, and AgNO.sub.3 at a ratio of (1-2x):x:x (in
Example 1, x=0.2) to obtain precipitates of diethyldithiocarbamate
(complex
Zn.sub.(1-2x)In.sub.xAg.sub.x(S.sub.2CN(C.sub.2H.sub.5).sub.2).sub.2)
(refer to the equation (1) below). The resultant complex was washed
with methanol and dried under a reduced pressure to prepare a
powder. Then, 50 mg of the powder was placed in a test tube which
was then purged with argon, and heated at 180.degree. C. for 30
minutes under stirring with a magnetic stirrer bar to heat-treat
the complex. As the heating temperature, the temperature of an
aluminum block surrounding the test tube was measured. As a result,
semiconductor nanoparticles (Zn.sub.(1-2x)In.sub.xAg.sub.xS) were
produced (refer to the equation (2) below). Then, the semiconductor
nanoparticles were cooled to room temperature, and 0.5 g of
hexadecylamine was added as an alkylamine. After argon purging, the
semiconductor nanoparticles were heated again at 180.degree. C. for
30 minutes under stirring to chemically modify the surfaces of the
semiconductor nanoparticles with hexadecylamine. In this step, the
semiconductor nanoparticles chemically modified with hexadecylamine
were dispersed in excessive hexadecylamine which was solid at room
temperature. Although, in this specification, the semiconductor
nanoparticles are denoted by Zn.sub.(1-2x)In.sub.xAg.sub.xS, this
is a convenient notation based on the atomic number ratio (molar
ratio) of the metals used for preparing the complex. The actually
prepared semiconductor nanoparticles do not necessarily satisfy the
composition formula ZnInAg.sub.xS and possibly include
nanoparticles with other compositions.
(1-2X)Zn.sup.2+, xIn.sup.3+,
xAg.sup.++(C.sub.2H.sub.5).sub.2NCS.sub.2.sup.-.fwdarw.Zn.sub.(1-2x)In.su-
b.xAg.sub.x(S.sub.2CN(C.sub.2H.sub.5).sub.2).sub.2 (1)
Zn.sub.(1-2x)In.sub.xAg.sub.x(S.sub.2CN(C.sub.2H.sub.5).sub.2).sub.2.fwd-
arw.Zn.sub.(1-2x)In.sub.xAg.sub.xS+diethyldithiocarbamic acid
decomposition product (2)
EXAMPLE 2
[0042] Semiconductor nanoparticles chemically modified with
hexadecylamine were synthesized by the same method as in Example 1
except that x=0.3 to obtain the semiconductor nanoparticles
dispersed in excessive hexadecylamine (solid at room
temperature).
EXAMPLE 3
[0043] Semiconductor nanoparticles chemically modified with
hexadecylamine were synthesized by the same method as in Example 1
except that x=0.5 to obtain the semiconductor nanoparticles
dispersed in excessive hexadecylamine (solid at room temperature).
In this case, since x=0.5, the semiconductor nanoparticles were
represented by In.sub.0.5Ag.sub.0.5S.
EXAMPLE 4
[0044] [Properties of Semiconductor Nanoparticles of Examples 1 to
3]
1. Emission Characteristics
[0045] An emission spectrum of the semiconductor nanoparticles
obtained in each of Examples 1 to 3 was measured. Namely, when the
semiconductor nanoparticles chemically modified with hexadecylamine
were dispersed in excessive hexadecylamine (solid at room
temperature), the solid of any one of Examples 1 to 3 was brown
under room light, but strong luminescent light was emitted by
irradiation with ultraviolet light (wavelength 350 nm) at room
temperature. The color of emitted light changed to green, yellow,
and red as the x value increased to 0.2, 0.3, and 0.5,
respectively. On the other hand, since the semiconductor
nanoparticles produced in each of Examples 1 to 3 were dispersed in
excessive hexadecylamine which was solid at room temperature,
1-butanol was added to dissolve the excessive hexadecylamine, and
then the product was centrifuged to obtain semiconductor
nanoparticles chemically modified with hexadecylamine as
precipitates. The resultant precipitates were suspended in
1-butanol and irradiated with ultraviolet light (wavelength 400 nm)
at room temperature, followed by measurement of emission spectra.
As a result, as shown in FIG. 1, the emission peak shifted to long
wavelengths of 550 nm, 580 nm, and 720 nm as the ratios of In and
Ag used for synthesis increased, i.e., the x value increased to
0.2, 0.3, and 0.5, respectively.
[0046] 2. TEM Observation
[0047] The semiconductor nanoparticles obtained in Example 1 were
observed with a transmission electron microscope (TEM, 2010F model
manufactured by JEOL, Ltd.). The results are shown in FIG. 2. FIG.
2(b) is a partially enlarged view of FIG. 2(a). As a TEM grid, a
commercial carbon deposited micro grid (Okenshoji type B) was used.
Since the semiconductor nanoparticles produced in Example 1 were
dispersed in excessive hexadecylamine which was solid at room
temperature, methanol was added to dissolve the excessive
hexadecylamine and remove it by centrifugal separation. The
resultant precipitates were further washed with methanol and then
suspended in methanol. The resultant suspension was dropped on the
TEM grid and then dried to form a sample. As a result of TEM
observation of the sample, rod-shaped particles were observed in
addition to many spherical particles (refer to FIG. 2). In a
high-resolution image of the semiconductor nanoparticles, clear
lattice fringes were observed. It was thus found that each
nanoparticle is a particle with high crystallinity. As a result of
composition analysis of the particles by an energy dispersive X-ray
analyzer (EDX), any one of the particles contained all of Zn, In,
Ag, and S. Although the ratio of the number of atoms of S contained
in the particles was substantially constant at about 50% regardless
of the particles prepared, the content ratios of the metal
elements, i.e., Zn, In, and Ag, varied between 21 to 31%, 7 to 16%,
and 5 to 11%, respectively, according to the particles. The
particle size distribution of the spherical particles according to
the TEM images was as shown in FIG. 3. This indicates that the
particle sizes are distributed from 5 nm to 15 nm, the average
particle size is 8.8 nm, and the standard deviation is 1.9 nm.
[0048] 3. Composition Analysis of Complex
[0049] The composition of the
Zn.sub.1-2xIn.sub.xAg.sub.x(S.sub.2CNEt.sub.2).sub.2 complex
(x=0.2, 0.3, or 0.5) was analyzed. The complex obtained in the
course of production of the semiconductor nanoparticles in each of
Examples 1 to 3 was washed with methanol several times and then
dried under a reduced pressure to form a measurement sample. The
results of composition analysis are shown in Table 1. In Table 1,
each of the theoretical values and analysis values is represented
by % by weight. Table 1 indicates that in any one of the complexes,
the analysis values of S, C, N, and H elements sufficiently agree
with the theoretical values regardless of the x values. This
reveals that the
Zn.sub.1-2xIn.sub.xAg.sub.x(S.sub.2CNEt.sub.2).sub.2 complex having
a chemical composition based on the ratio of the elements charged
can be produced.
TABLE-US-00001 TABLE 1 x = 0.2 x = 0.3 x = 0.5 theoretical analysis
theoretical analysis theoretical analysis element value value value
value value value S 33.73 33.50 32.93 32.60 31.45 30.94 C 31.58
31.38 30.84 30.55 29.45 29.00 N 7.37 7.32 7.19 7.15 6.87 6.71 H
5.30 5.04 5.18 4.97 4.94 4.65
EXAMPLE 5
[0050] Semiconductor nanoparticles (x=0.2) chemically modified with
oleylamine were synthesized by the same method as in Example 1
except that oleylamine was used as an alkylamine. However,
oleylamine was liquid at room temperature, and thus the procedures
were as follows: The surfaces of the semiconductor nanoparticles
were chemically modified with oleylamine, and then precipitates
were separated from a supernatant by centrifugal separation. Then,
3 cm.sup.3 of methanol was added to the supernatant to precipitate
the semiconductor nanoparticles chemically modified with
oleylamine. The precipitates were isolated by centrifugal
separation to remove excessive oleylamine. Then, 1 cm.sup.3 of
chloroform was added to the resultant precipitates to again
dissolve them. This operation (precipitation by adding methanol and
re-dissolution in chloroform) was repeated two times to prepare a
chloroform solution of the semiconductor nanoparticles chemically
modified with oleylamine.
EXAMPLE 6
[0051] Semiconductor nanoparticles chemically modified with
oleylamine were synthesized by the same method as in Example 5
except that x=0.3, and precipitates were separated from a
supernatant by centrifugal separation. Also, a chloroform solution
of the semiconductor nanoparticles was prepared.
EXAMPLE 7
[0052] Semiconductor nanoparticles chemically modified with
oleylamine were synthesized by the same method as in Example 5
except that x=0.5, and precipitates were separated from a
supernatant by centrifugal separation. Also, a chloroform solution
of the semiconductor nanoparticles was prepared.
EXAMPLE 8
[0053] [Properties of Semiconductor Nanoparticles of Examples 5 to
7]
1. Emission Characteristics of Supernatant and Precipitates
[0054] The supernatant and precipitates of the semiconductor
nanoparticles chemically modified with oleylamine were irradiated
with ultraviolet light (350 nm) at room temperature. In both the
supernatant and the precipitates, strong luminescent light was
emitted. The luminescent color was changed to green, yellow, and
red as the x value was increased to 0.2, 0.3, and 0.5,
respectively.
[0055] FIG. 4 shows emission and excitation spectra of the
supernatant (solution of the semiconductor nanoparticles chemically
modified with oleylamine in excessive oleylamine) of the
semiconductor nanoparticles chemically modified with oleylamine.
FIG. 4(a) shows excitation spectra, and FIG. 4(b) shows emission
spectra. FIG. 4(a) indicates that each excitation spectrum has wide
absorption on the shorter wavelength side than the absorption onset
and thus shows a light absorption behavior peculiar to
semiconductors. Further, an onset wavelength was determined by
extrapolating a linear portion. As a result, it was found that the
onset wavelength shifts to the long wavelengths of 500, 520, and
644 nm as the x values increases to 0.2, 0.3, and 0.5,
respectively. Further, an exciton absorption peak was observed as
shown by an arrow, and was found to shift to longer wavelengths as
the x value increases. On the other hand, in the emission spectra
shown in FIG. 4(b), the emission peak of oleylamine used as a
solvent is observed at 430 nm, but the emission peak of the
Zn.sub.(1-2x)In.sub.xAg.sub.xS nanoparticles shifts to longer
wavelengths of 530, 560, and 670 nm as the x values increases to
0.2, 0.3, and 0.5, respectively.
[0056] FIG. 5 shows emission spectra of the semiconductor
nanoparticles chemically modified with oleylamine (the particles
precipitated in oleylamine). Like the supernatant, in these
emission spectra, the emission peak shifts to the longer wavelength
side as the x value of Zn.sub.(1-2x)In.sub.xAg.sub.xS increases to
0.2, 0.3, and 0.5, respectively. However, in a comparison between
the emission peaks with the same x value, the emission peak of the
precipitates is positioned on the longer wavelength side than that
of the uniform solution of the nanoparticles. This indicates that
the two samples (supernatant and precipitates) have different
Zn.sub.(1-2x)In.sub.xAg.sub.xS nanoparticle sizes. It is also known
that the energy gap of semiconductor nanoparticles increases due to
the quantum size effect as the particle size decreases, and the
emission wavelength decreases as the nanoparticle size decreases.
Therefore, these results suggest that the precipitated particles
have a larger particle size.
[0057] 2. Purification and Emission Behavior in Chloroform
[0058] Absorption and emission spectra of the chloroform solution
(containing the Zn.sub.(1-2x)In.sub.xAg.sub.xS (x=0.5)
semiconductor nanoparticles chemically modified with oleylamine)
obtained in Example 7 were measured at room temperature. The
results are shown in FIG. 6. FIG. 6(a) shows absorption spectra,
and FIG. 6(b) shows emission spectra. FIG. 6 indicates that as well
as the absorption spectra, the emission spectra are substantially
the same regardless of the solvent used. This suggests that the
nanoparticles are stably present without aggregation even after
separation and purification operations. It is also found that the
absorption spectrum rises at about 700 nm, and the rising
wavelength substantially agrees with the emission peak wavelength.
Further, an increase in absorbance due to light scattering as shown
by secondary particles is not observed in the wavelength region of
700 nm or more. Therefore, it is found that the nanoparticles are
uniformly dissolved in any solvent (uniformly dispersed without
forming secondary particles).
[0059] 3. Quantum Yield
[0060] The emission quantum yield of the
Zn.sub.(1-2x)In.sub.xAg.sub.xS (x=0.5) nanoparticles in the
chloroform solution obtained in Example 7 was determined by a
relative method at room temperature using the fact that the
fluorescence quantum yield (the ratio the number of photons emitted
by luminescence to the number of photons absorbed) of fluorescein
in a 0.1 moldm.sup.-3 NaOH aqueous solution is 0.92. As a result,
the quantum yield was about 0.1, indicating that the nanoparticles
emit light with a relatively high efficiency.
[0061] 4. Influence of Chemical Modification Time After Addition of
Amine on Emission Spectrum
[0062] The time of chemical modification (reaction temperature
180.degree. C.) with oleylamine was changed to examine the
influence on the emission characteristics of the produced
particles. Although, in Example 7, the chloroform solution was
prepared by chemical modification at 180.degree. C. for 3 minutes,
in this example, a chloroform solution was prepared by chemical
modification at 180.degree. C. for 10 minutes. As a result of the
measurement of emission spectra of both solutions at room
temperature, it was found that as shown in FIG. 7, the peak
wavelength shifts to the longer wavelength side as the reaction
time increases. This is possibly due to the phenomenon that
particle growth is accelerated by increasing the heating time to
produce larger nanoparticles, thereby deceasing the degree of the
quantum size effect.
[0063] 5. Influence of Reaction Temperature of Surface Chemical
Modification With Amine
[0064] In order to examine the influence of the reaction
temperature of surface chemical modification of particles,
Zn.sub.(1-2x)In.sub.xAg.sub.xS (x=0.5) nanoparticles were produced
by chemical modification at 150.degree. C. in oleylamine or
octylamine. When oleylamine was used, the chloroform solution
prepared by chemical modification at 180.degree. C. in Example 7
emitted strong luminescent light at room temperature, while the
chloroform solution prepared by chemical modification at
150.degree. C. emitted little photo luminescence at room
temperature. On the other hand, when octylamine was used, the
chloroform solution prepared by chemical modification at
150.degree. C. emitted strong luminescent light at room
temperature. FIG. 8 shows the resultant emission spectrum (a in
FIG. 8) together with the result (b in FIG. 8) of the semiconductor
nanoparticles chemically modified with oleylamine at 180.degree. C.
In the case of chemical modification with octylamine at a lower
temperature, the emission peak wavelength shifts to the shorter
wavelength side. This is possibly due to the suppression of
particle growth at a lower surface treatment temperature.
[0065] 6. Formation of Nanoparticles by Heat Treatment of Complex
in Coexistence With Amine
[0066] In Examples 1 to 6, the complex was heat-treated, and then
the particle surfaces were chemically modified with an amine to
produce the Zn.sub.(1-2x)In.sub.xAg.sub.xS nanoparticles (referred
to as the "sequential method"). As in Example 7, in this example,
the complex with x=0.5 was suspended in oleylamine and then heated
at 180.degree. C. for 30 minutes to form semiconductor
nanoparticles and chemically modify the surfaces of the particles
at the same time (referred to as the "simultaneous method"). FIG. 9
shows emission spectra of the resultant particles at room
temperature. The nanoparticles produced by the simultaneous method
showed a slightly sharp spectrum, but no significant change was
observed in the emission peak wavelength.
[0067] 7. Crystal Structure of Nanoparticles
[0068] The crystal structure of Zn.sub.1-2xIn.sub.xAg.sub.xS.sub.2
nanoparticles was determined by XRD measurement using a powder
X-ray diffraction measurement apparatus (Rigaku Industrial
Corporation, RINT2100). FIG. 10 shows the obtained XRD patterns. A
measurement sample was prepared as follows: Methanol was added to
the oleylamine solution of the nanoparticles (the nanoparticles
produced by heating together with oleylamine) which were prepared
in each of Examples 5 to 7 to precipitate the nanoparticles. Then,
the precipitates were separated by centrifugation and then
dissolved in chloroform. Then, methanol was again added to
precipitate the nanoparticles, and the precipitates were recovered
by centrifugation. The precipitates were washed with methanol
several times and then dried under a reduced pressure to obtain
Zn.sub.1-2xIn.sub.xAg.sub.xS.sub.2 nanoparticles. Nanoparticles
with x=0 (i.e., ZnS nanoparticles) were prepared by the same method
as described above.
[0069] FIG. 10 indicates that in any type of nanoparticles, three
large peaks were observed in a 2.theta. region of 25.degree. or
more regardless of the x value, and thus these nanoparticles have
similar crystal structures. Any one of the three peaks shifts to
the lower angle side as the x value increases. This tendency well
agrees with the results reported by Kudo et al. using synthesized
bulk Zn.sub.1-2x(AgIn).sub.xS particles (J. Am. Chem. Soc., vol.
126, p. 13406 (2004)). Also, this suggests that the distance of
lattice planes of the nanoparticles increases as the x value
increases. For ZnS, hexagonal (wurtzite type) and cubic (sphalerite
type) crystal structures are known. Therefore, in a comparison
between the XRD patterns of the known crystal structures (refer to
FIG. 11) and the XRD pattern with x=0 (refer to FIG. 10), the
resultant ZnS nanoparticles show very broad diffraction peaks, but
the peak positions and intensities well agree with those of
reported cubic structure ZnS. On the other hand, for AgInS.sub.2,
tetragonal, rhombic, and rhombohedral crystal structures are known.
Therefore, in a comparison between the XRD patterns of the known
crystal structures (refer to FIG. 12) and the XRD pattern with
x=0.5 (refer to FIG. 10), the resultant AgInS.sub.2 nanoparticles
show very broad diffraction peaks, but the peak positions and
intensities well agree with those of reported tetragonal structure
AgInS.sub.2. Since the crystal structures of tetragonal AgInS.sub.2
and cubic (sphalerite type) ZnS have the same relative positional
relation between cation (metal ion) and anion (sulfide ion), it is
suggested that the relative positional relation between cation
(metal ion) and anion (sulfide ion) in the crystal structure of the
resultant Zn.sub.1-2xIn.sub.xAg.sub.xS nanoparticles is the same as
that of these two crystal structures.
EXAMPLE 9
[0070] Nine types of Zn.sub.1-2xIn.sub.xAg.sub.xS nanoparticles
with x=0, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.48, and 0.5 were
prepared according to the method in Example 5, and each type of
nanoparticles was dissolved in chloroform to measure emission using
exciting light at 350 nm. FIG. 13 shows a relation between the
emission peak position and x value. FIG. 13 indicates that the
emission peak wavelength shifts from 430 nm to a longer wavelength
of 690 nm as the x value increases from 0.02 to 0.48. This result
reveals that emission of blue light to red light can be achieved by
changing the x value of Zn.sub.1-2xIn.sub.xAg.sub.xS nanoparticles
in the range of 0<x<0.5.
EXAMPLE 10
[0071] Zn.sub.1-2xIn.sub.xCu.sub.xS (x=0.2) nanoparticles were
prepared as follows: First, 500 ml of an aqueous solution
containing 0.4 mmolmol.sup.-3 of Et.sub.2NCS.sub.2Na.3H.sub.2O
(Wako, extra-pure reagent) was prepared. Also, 500 ml of an aqueous
solution containing 0.080 mmoldm.sup.-3 of CuCl (Kishida,
extra-pure reagent), 0.080 mmoldm.sup.-3 of InCl.sub.3.4H.sub.2O
(Wako), and 0.24 mmoldm.sup.-3 of ZnCl.sub.2 (Kishida, extra-pure
reagent) was prepared. The former solution was placed in a 1000-ml
eggplant-type flask, and the latter solution was slowly added
thereto under stirring. After stirring for 20 minutes, the produced
precipitates were recovered by centrifugation and then washed with
ion exchanged water three times and methanol (Wako, extra-pure
reagent) two times. The resultant precipitates were dried under a
reduced pressure to recover 0.02 g of brown precipitates
(Zn.sub.1-2xIn.sub.xCu.sub.x(S.sub.2CNEt.sub.2).sub.2) complex).
Then, 0.018 g of the thus-obtained complex was placed in a test
tube, and the test tube was sealed after the vapor phase was purged
with nitrogen for 10 minutes. The test tube was heated at
180.degree. C. for 30 minutes under stirring. After air cooling, 3
cm.sup.3 of oleylamine (Tokyo Chemical Industry Co., Ltd.) was
added to the test tube, and the test tube was sealed after bubbling
with nitrogen for 10 minutes, followed by heating and stirring at
180.degree. C. for 30 minutes. After air cooling, the supernatant
was recovered by centrifugation, and methanol (Wako, extra-pure
reagent) was added thereto to precipitate the particles dissolved
in oleylamine. The produced precipitates were recovered by
centrifugation and dissolved in chloroform (Wako, extra-pure
reagent), and methanol was again added thereto to precipitates the
particles, thereby removing impurities. The produced precipitates
(Zn.sub.1-2xIn.sub.xCu.sub.xS (x=0.2) nanoparticles) were recovered
by centrifugation and dissolved in chloroform, and absorption and
emission spectra were measured. FIG. 14(a) shows the absorption
spectrum of the nanoparticles, and FIG. 14(b) shows the emission
spectrum thereof.
[0072] FIG. 14(a) shows absorption rising at 720 nm. Also, FIG.
14(b) shows strong light emission at 730 nm. Since the emission
peak substantially coincides with the absorption onset wavelength
of the particles, the emission is found to be band gap emission of
(CuIn).sub.xZn.sub.1-2xS (x=0.2) particles.
[0073] The present invention is not limited to the above-described
examples, and, of course, the invention can be carried out in
various modes within the technical scope of the present invention.
This application claims priority of Japanese Patent Application No.
2005-255656 filed on Sep. 2, 2005, the entire contents of which are
incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0074] The semiconductor nanoparticles of the present invention can
be used as a material for vital staining dyes and optical devices
such as white LED by using the emission characteristics.
* * * * *